The invention relates to a method and to a welding torch for tungsten inert gas welding, wherein an arc burns between a non-consumable electrode and a work piece, wherein the electrode in its interior comprises a cavity and wherein an electrically conductive filler is fed through the cavity of the electrode in the direction of the work piece.
Tungsten inert gas welding (TIG-welding) is an arc welding method, which is used for example for deposition welding, welding or brazing of one, two or more work pieces made of metallic materials. The work piece and a tungsten electrode of a suitable welding torch for tungsten inert gas welding are electrically connected to a welding current source. An arc burns between the tungsten electrode and the work piece. Here, the work piece is at least partially melted and there forms the melt pool. The tungsten electrode is mostly used as cathode and the work piece as anode, while electrons from the tungsten electrode migrate into the material.
In contrast with metal inert gas welding (MIG-welding), the tungsten electrode does not melt in tungsten inert gas welding. The melting of a wire electrode in a welding torch for metal inert gas welding can result in overheating and evaporation of said wire electrode, as a result of which large quantities of harmful emissions in the form of welding fumes are liberated. Welding fumes consist of particulate pollutants (mostly metal oxides), which can be inhalable and respirable as well as toxic and/or carcinogenic. Such emission particles are particularly harmful to a welder.
In metal inert gas welding, molten, drops of the wire electrode pass into the melt pools. The melting wire electrode in metal inert, gas welding simultaneously serves as filler or filler material and as arc carrier. In tungsten inert as welding, by contrast, a filler has to be additionally supplied. This (for example wire-shaped) filler is laterally introduced into the arc. Because of this, the filler is melted. Liquid molten drops of this filler detach and pass into the melt pool. This process of melting of the filler, formation of the drop, detaching of the drop and interaction of the drop with the work piece is called material transfer.
In metal inert gas welding, a large part of the energy for melting the wire electrode is introduced by electrons, which pass from the wire electrode into the work piece. This energy introduced by the electrons is called condensation. This energy is fed in by way of a comparatively small area (namely by way of the arc attachment) and to a major part contributes to the overheating and evaporation of the wire electrode and thus to the liberation of the particulate emissions.
Since in tungsten inert gas welding the filler is introduced into the arc without current, the filler is heated only through heat conduction and convection. Condensation, i.e. energy introduced by electrons, does not play a role in tungsten inert gas welding. Consequently, there is no or hardly any overheating and evaporating of the filler in tungsten inert gas welding.
Consequently, the tungsten inert gas welding compared with the metal inert gas welding has the advantage that only a very low quantity of emissions is liberated and in particular hardly any welding fumes are created, even when filler is introduced from the outside. On the other hand, the tungsten inert gas welding compared with metal inert gas welding has the disadvantage that the melting of the filler takes place with a low efficiency or a lower rate of melting than is the case in metal inert gas welding. Furthermore, because of the absent current flow through the filler, no electromagnetic forces such as Lorentz forces can develop either. Such electromagnetic forces favour the detaching of molten drops in the case of fillers through which current flows, which is called “pinching off”. Since the in particular wire-shaped filler is mostly laterally fed to the arc, the rotation symmetry of the welding torch is additionally lost.
The tungsten electrode in tungsten inert gas welding can for example be formed as a hollow electrode or hollow cathode. Such a hollow electrode has a cavity in its interior. In particular, this cavity extends over the complete axial extent of the electrode.
Such a hollow electrode is known for example from EP 2 457 681 A1. Therein it is described that a filler can be fed through the cavity of the hollow electrode to tungsten inert gas welding. Because of this, the disadvantage of the absent rotation symmetry can be rectified, but the disadvantages of the low efficiency of the melting of the filler or of the low melting efficiency remains.
In addition to this, the melting of the filler is rendered more difficult in particular in the case of hollow electrodes since the cavity in the hollow electrode also results in a lower axial energy density in the arc. In addition, no electromagnetic forces occur with such a fed-in filler either and no energy is introduced by electrons.
The invention is therefore based on the object of improving the feeding of a filler in tungsten inert as welding and carrying out the same with a higher efficiency.